Most Earth-like exoplanet started out as Saturn-sized gas giant

Washington, January 7 (ANI): A new research has indicated that the most Earth-like planet yet found around another star may be the rocky remains of a Saturn-size gas giant.

The planet in question is CoRoT-7b, the smallest planet and the most like Earth that astronomers have found to date.

Discovered in February 2009 by the Convection, Rotation and Planetary Transits (CoRoT) satellite, a mission led by the French Space Agency, CoRoT-7b takes just 20.4 hours to circle its Sun-like star, located 480 light-years away in the constellation Monoceros.

Astronomers believe the star is about 1.5 billion years old, or about one-third the Sun's age.

"CoRoT-7b is almost 60 times closer to its star than Earth, so the star appears almost 360 times larger than the Sun does in our sky," said Brian Jackson from NASA's Goddard Space Flight Center in Greenbelt, Maryland.

As a consequence, the planet's surface experiences extreme heating that may reach 3,600 degrees Fahrenheit on the daylight side.

CoRoT-7b's size (70 percent larger than Earth) and mass (4.8 times Earth's) indicate that the world is probably made of rocky materials.

"But with such a high dayside temperature, any rocky surface facing the star must be molten, and the planet cannot retain anything more than a tenuous atmosphere, even one of vaporized rock," Jackson said.

With the help of computer models that track the planet's mass loss and orbital changes, the researchers have turned back the planet's clock.

"There's a complex interplay between the mass the planet loses and its gravitational pull, which raises tides on the star," Jackson explained.

Those tides gradually change the planet's orbit, drawing it inward in a process called tidal migration.

But closer proximity to the star then increases the mass loss, which in turn slows the rate of orbital change.

After accounting for the give-and-take of mass loss and tidal migration, the team found that CoRot-7b could have weighed in at 100 Earth masses - or about the heft of Saturn - when it first formed.

At that time, it orbited 50 percent farther from its star than it does now.

The researchers also show that regardless of whether CoRot-7b started life as a Saturn-like gas giant or as a rocky world, the planet has probably lost many Earth masses of material since its formation.

"You could say that, one way or the other, this planet is disappearing before our eyes," Jackson said. (ANI)